1. Field of the Invention
The present invention relates to a dental treating apparatus with a hand piece, more specifically, to a dental treating apparatus that causes a cutting tool for cutting and enlarging an inner wall of a root canal of a tooth to be driven.
2. Description of the Background Art
As for a dental treating apparatus with a hand piece, there is, for example, an apparatus for providing treatment by attaching a cutting tool to a head unit of a hand piece and driving the cutting tool to cut and enlarge a root canal of a tooth. U.S. Pat. No. 3,264,607 (PTL 1), U.S. Pat. No. 3,676,753 (PTL 2) and U.S. Pat. No. 3,615,209 (PTL 3) disclose various types of driving control in order to, for example, prevent breakage due to a load applied to the cutting tool when the dental treating apparatus causes the cutting tool to be driven to cut and enlarge the root canal of the tooth.
A dental treating apparatus disclosed in PTL 1 includes detecting means for detecting a load applied to a cutting tool, and control means for reversely rotating a cutting tool driving motor when the detected load reaches a preset reference.
A dental treating apparatus disclosed in PTL 2 includes driving means for driving a cutting tool, load detecting means for detecting a load applied to the cutting tool, root canal length measuring means for measuring a root canal length by using the cutting tool, reference load setting means for arbitrarily presetting a reference load, and control means for controlling the driving means. When the load detected by the load detecting means exceeds the reference load, the control means controls the driving means by any one of the operations of stopping driving of the cutting tool, reducing an amount of driving, reversing rotation, and repeating normal rotation and reverse rotation, such that the load applied to the cutting tool is reduced. Furthermore, based on a value of the root canal length measured by the root canal length measuring means, the control means controls the driving means such that the amount of driving the cutting tool becomes smaller as a distance from the cutting tool to a root apex becomes shorter.
A dental treating apparatus disclosed in PTL 3 includes driving means for driving a cutting tool, root canal length measuring means for measuring a root canal length, and control means for controlling the driving means such that the driving force of the cutting tool changes in accordance with a value of the root canal length measured by the root canal length measuring means. The control means includes number-of-rotations control means for controlling the number of rotations of the cutting tool. Based on the value of the root canal length measured by the root canal length measuring means, the number-of-rotations control means controls the driving means such that the number of rotations of the cutting tool becomes smaller as a distance from the cutting tool to a root apex becomes shorter.
In addition to a cutting tool having a blade formed such that the cutting tool is rotated in one direction to cut a tooth, there has recently been a cutting tool having a blade formed such that the cutting tool is rotated alternately in one direction and in the opposite direction to cut a tooth. Japanese National Patent Publication. No. 2003-504113 (PTL 4) discloses a dental treating apparatus that causes the cutting tool to be driven to rotate alternately in one direction and in the opposite direction.
In the dental treating apparatus disclosed in PTL 4, the cutting tool is rotated clockwise or counterclockwise by a desired first rotation angle, and subsequently, is rotated in a direction opposite to the first rotation angle by a second rotation angle. The first rotation angle is larger than the second rotation angle such that a cut piece is discharged from a surface of a root canal to the above.
The root canal of the tooth, which is an object to be cut, is thin and curved. Therefore, the cutting tool of the dental treating apparatus must be inserted into the curved root canal to cut and enlarge the root canal. A highly-flexible nickel titanium alloy and the like are used as a material of the cutting tool to cut and enlarge the curved root canal. However, application of excessive load results in breakage of the cutting tool. Therefore, the cutting tool of the dental treating apparatus must be driven such that the excessive load is not applied to the cutting tool.
If the excessive load is applied and the cutting tool is broken when the cutting tool is cutting and enlarging the root canal of the tooth, the tooth must be cut more than necessary in order to remove the cutting tool from the root canal. Furthermore, if the cutting tool cannot be removed from the root canal, the tooth itself must be drawn.
As for the dental treating apparatus that causes the cutting tool to be driven with normal driving in which the cutting tool is rotated in one direction, PTLs 1 to 3 suggest control for driving the cutting tool such that the excessive load is not applied. However, as for the dental treating apparatus that causes the cutting tool to be driven with twist driving in which the cutting tool is rotated alternately in one direction and in the opposite direction, PTL 4 and the like do not suggest control for driving the cutting tool such that the excessive load is not applied.